Little bugs on the prairie: the key to happy grassland

To fix a damaged ecosystem you need to start from the ground up – with the microbes that live in the soil. The first step in that direction has been taken for the tallgrass prairies of the US Midwest – a once fertile landscape now described as a near-extinct biome.

Ecologists who restore endangered ecosystems traditionally focus on bringing back native animals and plants, but a growing body of evidence is revealing the crucial roles that soil microbes play in ecosystem stability. They break down organic matter, recycle nutrients, and can influence plant health and productivity. However, with the exception of nitrogen-fixing root fungi, microorganisms have largely been ignored in ecosystem restoration projects.

Unsung heroes

“With wetland reconstruction, for example, there’s a very clear set of monitoring criteria which you have to abide by, and none of them has anything to do with microbes,” says Angela Kent, a microbial ecologist with the University of Illinois at Urbana-Champaign. That’s partly because microbes aren’t easy to quantify or characterise, she says. “For most of these ecosystems, we don’t even have a good idea of what a target community would look like.”

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Noah Fierer of the University of Colorado at Boulder decided to try and get an idea of how such a community might look for the tallgrass prairies – a once highly productive, lush landscape now degraded thanks to intense farming.

“They were the most fertile soils that existed in North America,” says Fierer. “Problem is, those soils don’t exist any more. They’ve been ploughed under and subjected to centuries of growing corn.”

By comparing topsoil taken from 31 uncultivated prairie sites, such as cemeteries and national parks, with soil from agricultural land, Fierer’s team identified a set of microbes that likely inhabited the untouched prairies and were lost when the soil was worked. The dominant group of bacteria is the Verrucomicrobia, thought to play an important role in carbon cycling. The hope is that Verrucomicrobia or other bacteria could help rejuvenate existing prairie.

“Now that we have a best guess of what native bacterial communities looked like, maybe we can start asking whether there are specific bugs we can use to accelerate restoration,” says Fierer.

Prairie probiotic

Inoculating restored habitats with beneficial bacteria is still some way off. The next step is to find out exactly what role the disappeared bacteria used to play in the soil; how they contributed to health and productivity of the prairie.

Future experiments will also need to assess the potential risks of changing the composition of a soil’s microbial community.

“There might be risks, but I would guess that they wouldn’t be very large,” says biologist Jim Bever of Indiana University Bloomington. “Those microbes, and even some pathogens, coexisted stably with those plants in the original, pre-agricultural condition.”